I would like to take a survey (of those willing to share) of wheel base designs. The idea we’re pursuing is a six wheel drive in which the forward and aft wheels pivot about the center so that our bot will conform to the bump as we go over. I’m wondering if anyone else has similar ideas. If not, what do you guys think of such an idea? I’ve seen several posts on it throughout the forum, but I don’t see a strong consensus whether or not it would be an effective design.
I am particularly worried about the robot flipping so that is why were pursuing the articulated drivebase. Do you guys agree that this design will help?
816 is using an 8WD with 6" wheels on approximately 10" wheelbases with the center 4 wheels dropped 3/16" in a long base configuration.
After doing a bit of 3D work with the design and then seeing it as a rolling chassis, I am fully confident in it’s ability to climb the bump should we be able to keep our center of gravity low enough. None of the other mentors on my team felt that articulation in the drive train was necessary for navigating the bump and if anything it would add unnecessary weight to the robot. My personal opinion is that Articulation is not needed for most drive trains this year.
Should you want to go in the direction of an articulated drive I would see if you could get away with only having one pair of your 6 wheels articulate, either the forward or the aft. If you’re truly worried about tipping, there are probably some better options for your design than building a complicated drive train.
One thing to kep in the back of your mind: going up the ramp is the easy part, it is going down the other side that is hard. When my team built the kit bot and hand drove it over the bump, it went up fine; on the way down 4 out of 5 times it flipped. If I were looking at an articulated chassis I wouldn’t focus on designing it to go up, but rather get back on to the floor safely.
Food for thought:D
We’re doing one very similar, we spread the middle two wheels on each side to 12" centers, the end wheels are close together, and not as much drop. Initial tests rolling over the bump (pushing the robot from the center, and pushing down relative to Earth with some load to simulate the weight of the rest of the robot) look good.
8wd is not much different to build than 6wd, you mostly just need to buy two more wheels, bearings, sprockets, and axles.
We should have it driving in a few days.
Neat thing about 8wd vs 4wd is that it allows a lower center of gravity, which can make the robot less tippable, but it also allows the center of the robot to kind of roll over the bump. The 6wd does not naturally roll over a bump…it shoots way up in the air, then crashes down.